Transparentizing regenerated cellulose silk



Patented July 18, 1950 TRANSPARENTIZIN G REGENERATED CELLULOSE SILKErnst Weiss, Wattwil, Switzerland, assignor to Heberlein PatentCorporation, New York, N. Y., a corporation of New York No Drawing.Application December 22, 1945, Se-

rial No. 637,119. In Switzerland December 27,

4 Claims.

, 1 This invention relates to a process for transparentizing fibers andfabrics of regenerated cellulose.

Transparentizing of cotton fabrics by means of sulfuric acid is knownand has been used extensively commercially. 'Iransparentizing ofartificial silk, namely, regenerated cellulose silk fabrics withswelling agents is known, but due to the ease with which sulfuric acidand other swelling agents proposed attack the regenerated cellulose, ithas been difficult to control such processes to produce atransparentization, either in all-over or pattern effect, having thesame uniform appearance and high quality obtainable by the process asapplied to cotton. Attempts to secure greater uniformity and to lessenthe vigorous action of the sulfuric acid have been proposedby combiningwith the acid substances, such as monovalent or multivalent alcohols,heterocyclic bases, formaldehyde, ammonia salts, urea and theirderivative amino compounds. But these processes have not given thedesired results to produce a satisfactory commercial transparentizedviscose or other regenerated cellulose in transparent-form.

The principal object of the invention accordingly is to provide aprocess for the treatment of regenerated cellulose silk, such asviscose, which may be easily controlled to produce a transparentized,regenerated cellulose of high quality and appearance.

vI have found, unexpectedly in accordance with my invention, that theabove difliculties may be overcome by giving such fibers or fabrics atransparentizing treatment, followed by a treatment which has the resultof making the fabric appear more uniform and to give it a high qualityboth as to strength and appearance. This may be most satisfactorily doneby the use of caustic potash used, in accordance with my invention, at aregulated. range of temperature, time and concentration. And I havefound also that the caustic solution should be removed as rapidly aspossible, for example, by means of hot rinsing. The concentrations ofpotassium hydroxide which may be employed are preferably quite high,namely, of the order of 30 Baum. Room temperature is preferably used.Instead of caustic potash, caustic soda of a much lower concentrationmay be used, namely, 6 to less than 12 Baum'. Room temperature is alsoused. The treatment is followed by washing with boiling water toeliminate the caustic soda. The caustic alkali solutions-are used under.conditi'onsof time, temperature and concentration such that thesolutions areincapable of producing a parch- 2 mentizing effect on theoriginal untreated regenerated cellulose. The use of caustic potash andcaustic soda in the concentrations mentioned is in accordance with theknown solubilities of regenerated cellulose, such as viscose in aqueoussolutions of these alkalies. Potassium hydroxide has a far lowerdissolving power for regenerated cellulose, dissolving (when about 4.5 NKOI-I is used) only about 6% thereof as compared with for sodiumhydroxide (using about 2.5 N NaOI-I) at 0 C. In the case of both causticpotash and caustic soda solution, the dissolving power decreases as thetemperature rises. I take advantage of these facts, in accordance withmy invention, to avoid the use of either caustic potash or caustic sodain concentrations and at temperatures which will cause any substantialdissolving of regenerated cellulose material. In other words, afterapplying the sulfuric acid or other transparentizing treatment which initself constitutes a partial solution of the cellulose I avoid in theafter-treatment with the caustic a further dissolving action.Accordingly, I employ these caustic alkalies under conditions such thatthis second dissolving action is substantially avoided.

As a result I obtain transparentized regenerated cellulose which has auniform and otherwise pleasant appearance and is of high quality, i. e.,it has good wearing qualities and has a relatively soft feel, clueprobably to the fact that the second caustic treatment is not adissolving treatment since it appears that each dissolving treatmenttends to stiffen and otherwise impair the material somewhat. By myprocess only one such dis solving treatment is effected, and accordinglyonly a limited stiifening occurs.

My process is suitable for the production of both all-over effects andfor local transparent effects with the use of water-soluble orwaterinsoluble resists and with dyes or pigments a may be desired.

The process is applicable to the treatment of all fine fabrics made fromregenerated cellulose, such as spun rayon muslin or viscose muslin, orcorresponding voiles.

.As transparentizing or parchmentizing agents there may be used thewell-known cellulose swelling agents such as sulfuric acid (with orwithout additions) of over 42 Baum', phosphoric acid of over 50 Baum,hydrochloric acid of over 20 Baum, zinc chloride solutions of over 50Baum, calcium thiocyanate solutions of over 25 Baum, in which connectionthe requisite concentrations are in :addition dependent also upon thereaction temperature. By such transparentizing treatment, aparchmentized regenerated cellulose textile material results which lacksclarity and is non-uniform in appearance.

As above stated, for the subsequent treatment caustic potash solution ofabout 30 Baum at room temperature may be employed, or caustic sodasolution may be used in concentrations of 6 to less than 12 Baum withsubsequent rapid removal of the caustic to correct this lack of clarityand non-uniformity. The control of the process is more easily effectedby the use of caustic potash.

The following examples are illustrative of the process. It is to beunderstood that these examples are illustrative and the invention is notrestricted thereto except as indicated in the appended claims.

Examples 1. Viscose muslin which has been pre-cleansed by the usualmethods and dried under tension is passed in the broad state throughsulfuric acid of 48 Baum (measured at 15 0.). The temperature of theacid is kept between l C. and +l C.; the time of action amounts to 11seconds. Immediately thereafter the acid is washed out with .water atroom temperature, and any possible residues of acid are neutralizedbesides with dilute ammonia. The fabric is now freed from the excess ofwater by pressing or suction, and in still moist condition is thenexposed for 6 seconds to the action of caustic potash solution of 30Baum, freed from caustic by means of hot water at about 70 C., acidifiedwith sulfuric acid of 1 Baum, and washed. The material can now be eitherblued or dyed by the usual methods, whereupon it is dried under tensionin the directions of warp and weft; expediently it is further stenteredbefore the drying.

In this way one obtains an extensively translucent, comparatively butlittle stiffened fabric. The clarity and uniformity of the fabricpicture are considerably improved in comparison with a material that hasonly been parchmentized with acid.

2. Viscose muslin that has been imprinted with dyes fast to acid andfast to alkali is exposed for 12 seconds to the action of sulfuric acidcooled to C., whose specific gravity measured at 15 C. amounts to 47Baum, is then washed neutral and dried under tension. Now the materialis immersed for seconds at to C. in caustic potash solution of Baum,freed from caustic .with hot water (about 70 C.), acidified, and washeduntil a neutral reaction is attained. After pressing-off of the excesswater, the material is dried under tension. The drying of the materialcan be effected on a tension frame.

. After the above treatment sequence, one obtains a variegated fabricwith greatly increased transparency; in the imprinted parts a deepeningof color takes place.

3. A fabric produced from spun rayon of high wet tenacity, for example,No. 80 Eng, is desized, soaped, bleached, dyed, and dried on a tensionframe.

Now one passes it through a parchmentizing bath of the followingcomposition:

Per cent Sulfuric acid calculated as H2804 59.6 Urea 14.8

Water 25.6

.The temperature of the bath is kept at 25 C.;

the time of action amounts to 16 seconds. Tm mediately thereafter thematerial is washed cold, and the moist material is then subjected toaftertreatment with caustic potash solution of 28 Baum for 8 seconds atroom temperature. After the freeing from caustic and washing with hotwater, the material is stentered and dried under tension.Advantageously, the material is finally calendered besides.

Spun rayon muslin that has been treated in this manner corresponds inappearance to a highgrade cotton organdy.

4. Viscose spun rayon muslin is, in accordance with the usual methods,singed, desized, boiled, bleached, dried on a tension frame, andimprinted with a resist of the following composition:

Grams Titanium dioxide 260 Acetyl cellulose 40 Acetone 500 Phenol Water50 Now the material is exposed in the open width for 10 seconds to theaction of sulfuric acid of 47 Baum. In this process the temperature ofthe acid should be kept at 10 C. After the complete washing-out of theacid, the material is subjected to after-treatment with caustic potashsolution of 30 Baum for 6 seconds at room temperature, .washed hot,neutralized, and dried under tens1on.

In this way one obtains highly contrasting patterns of white opaqueprinted areas on a transparent ground.

5. Viscose voile is parchmentized at 10 C. for 15 seconds withphosphoric acid of 55 Baum (measured at 15 C.), and immediatelythereafter is subjected to after-treatment with caustic potash solutionas described in Example 4 and dried under tension.

There results an extensively transparentiz'ed, moderately stiffenedfabric.

6. Viscose marquisette is pre-cleansed by the well-known methods anddried on a tension frame. Now the material is passed in the open widththrough 60% sulfuric acid to which per liter 10 cc. of 40% technicalconcentrated formaldehyde have been added. The temperature of the acidshould be 0 C., the time of action 12 seconds. After the washing out ofthe acid, the material is dried under tension, whereupon it is subjectedto after-treatment with caustic soda solution of 8 Baum for 5 seconds,is washed hot, acidified, and thoroughly rinsed. Finally the fabric istensed in the warp and weft directions and dried.

An extensively transparent fabric is obtained.

7. A light weight fabric consisting in warp and weft of cuprammoniumsilk yarns is precleansed by the well-known methods and dried on atension frame. Now the material is treated in the open width for 12seconds with sulfuric acid of 475 Baum at a temperature of 0 C. Afterwashing out the acid the fabric is exposed for 6 seconds to the actionof caustic potash solution of 28 Baum, washed with hot water to removethe caustic, :acidulated with sulfuric acid of 1 Baum, washed until aneutral reaction .is attained, stentered and dried under tension.

There results a highly transparent, moderately stiffened fabric.

'8. Spun rayon muslin containing effect yarns or twists of cotton issinged, desized, boiled. bleached and dried on a tension frame. Now itis treated with sulfuric acid of 47 Baum as described in Example 4, andafter complete washing out of the acid, exposed to the action of causticsoda solution of Baum for 8 seconds, washed with hot water, acidifiedand washed until a neutral reaction is attained. Finally the fabric isstentered and dried under tension.

There results a transparent fabric containing nontransparentized effectyarns giving interesting optical contrasts.

The fabrics obtained in accordance with the above examples have auniform appearance where an all-over effect is obtained and the sameuniformity may be observed in the transparent patterned goods. Inaddition the goods are of high quality, are relatively soft, and ofmarketable character.

The expression regenerated cellulose material as employed in the claimsrefers to regenerated cellulose in the form of fiber, yarns, and fabricsof such material.

What I claim is:

1. A process which comprises treating regenerated cellulose with anaqueous solution selected from the group consisting of sulfuric acid ofabout 42 to about 48 B., phosphoric acid of about 50 to about 55 B.,hydrochloric acid of the order of B., zinc chloride of the order of 50 Band calcium thiocyanate of the order of B. for a period of time of theorder of 10 seconds at a temperature in a range of about roomtemperature and below, whereby an acid parchmentized regeneratedcellulose textile material results which lacks clarity and isnon-uniform in appearance, and treating such material substantially freefrom acid at room temperature with an aqueous caustic alkali solutionselected from the group consisting of potassium hydroxide of the orderof B. and sodium hydroxide at 6 to less than 12 B. for a period of theorder of 10 seconds to produce a clear uniform transparent fabric.

2. A process which comprises treating regenerated cellulose with anaqueous solution of sulfuric acid of about 42 to about 48 B. for aperiod of time of the order of 10- seconds at a temperature in a rangeof about room temperature and below, whereby an acid parchmentizedregenerated cellulose textile material results which lacks clarity andis non-uniform in appearance, and treating such material substantiallyfree from acid at room temperature with an aqueous caustic alkalisolution selected from the group consisting of potassium hydroxide ofthe order of 30 B. and sodium hydroxide at 6 to less than 12 B. for aperiod of the order of 10 seconds to produce a clear uniform transparentfabric.

3. A process which comprises treating regenerated cellulose with anaqueous solution of phosphoric acid of about 50 to about B. for a periodof time of the order of 15 seconds at a temperature in a range of aboutroom temperature and below, whereby an acid parchmentized regeneratedcellulose textile material results which lacks clarity and isnon-uniform in appearance, and treating such material substantially freefrom acid at room temperature with an aqueous solution of potassiumhydroxide of about 30 B. for a period of the order of 6 seconds toproduce a clear uniform transparent fabric.

4. A clear, uniform, transparent fabric of regenerated celluloseproduced by the process of claim 1.

ERNST WEISS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,558,453 Barrett Oct. 27, 19251,812,204 Hall June 30, 1931 1,985,124 Weiss Dec. 18, 1934 1,989,100Lilienfeld Jan. 29, 1935 1,989,101 Lilienfeld Jan. 29, 1935 1,998,577Heberlein Apr. 23, 1935 2,085,946 Bodmer et al July 6, 1937 2,174,534Shipp Oct. 3, 1939 2,200,792 Hefti May 14, 1940 2,202,200 Haller et a1.May 28, 1940 2,215,938 Schonholzer Sept. 24, 1940 2,245,123 Belloc June10', 1941 FOREIGN PATENTS Number Country Date 464,965 Great Britain Apr.28, 1937 516,843 Great Britain Jan. 12, 1940

1. A PROCESS WHICH COMPRISES TREATING REGENERATED CELLULOSE WITH ANAQUEOUS SOLUTION SELECTED FROM THE GROUP CONSISTING OF SULFURIC ACID OFABOUT 42* TO ABOUT 48*BE''., PHOSPHORIC ACID OF ABOUT 50* TO ABOUT55*BE''., HYDROCHLORIC ACID OF THE ORDER OF 20*BE''., ZINC CHLORIDE OFTHE ORDER OF 50*BE''. AND CALCIUM THIOCYANATE OF THE ORDER OF 25*BE''.FOR A PERIOD OF TIME OF THE ORDER OF 10 SECONDS AT A TEMPERATURE IN ARANGE OF ABOUT ROOM TEMPERATURE AND BELOW, WHEREBY AN ACID PARCHMENTIZEDREGENERATED CELLULOSE TEXTILE MATERIAL RESULTS WHBICH LACKS CLARITY ANDIS NON-UNIFORM IN APPEARANCE, AND TREATING SUCH MATERIAL SUBSTANTIALLYFREE FROM ACID AT ROOM TEMPERATURE WITH AN AQUEOUS CAUSTIC ALKALISOLUTION SELECTED FROM THE GROUP CONSISTING OF POTASSIUM HYDROXIDE OFTHE ORDER OF 30*BE''. AND SODIUM HYDROXIDE AT 6* TO LESS THAN 12*BE''.FOR A PERIOD OF ORDER OF 10 SECONDS TO PRODUCE A CLEAR UNIFORMTRANSPARENT FABRIC.